The objective of this project is to define the cellular and molecular basis for the potentiation of the cytotoxicity of nitrogen mustard (HN2) to leukemia cells observed following aminothiol pretreatment. The specific aims are based on the unique observation of potentiation in vivo of the cytotoxicity of HN2 following pretreatment of mice bearing AKR leukemia with the radiation protector WR-2721. Concomitant protection of normal hematopoetic stem cells (CFU-S) to HN2 cytotoxicity was observed. This potentiation of AKR leukemia has been shown to occur for a variety of other aminothiols, the most potent being disulfiram. No correlation has been noted between the ability of these agents to protect normal cells (CFU-S) from HN2 cytotoxicity and their ability to potentiate such cytotoxicity against leukemia cells. In this proposal, the generality of the potentiation will be examined using other murine leukemia and solid tumor models, specifically L1210 Leukemia, MOCP-315 plasmacytoma, Lewis Lung Carcinoma and Colon 36. A normal cell population the hematopoietic stem cell, will be examined also. A variety of aminothiols will be studied with particular emphasis on both dose-survival relationships for the most potent agents and scheduling studies examining both the 15' and 6 hr intervals. A number of alkylating agents will be examined including CCNU, L-PAM, cyclophosphamide and cis-platinium. Adriamycin and radiation will also be examined. The molecular basis for the potentiation will be studied by examining drug uptake as well as DNA damage and repair for a number of alkylating agents and the modulation of their cytotoxicity in both normal and maliganant cells by thiol pretreatment. An in vitro system for growth of both AKR leukemia and normal bone marrow has been established and the opposing effects of thiols on HN2 cytotoxicity observed in these two cell populations (potentiation and protection respectively) will be studied in vitro. Finally, intracellular thiol levels, both the exogenous agents and endogenous glutathione, will be modulated both in vivo and in vitro, assayed by HPLC, and the effect of such modulation examined and correlated with the above cellular and molecular findings. We expect to determine from these studies whether this findings has potential clinical therapeutic application.